Session Y04: Low-Frequency Gravitational Wave Astronomy

The Laser Interferometer Space Antenna: A space-based Gravitational Wave Observatory

After decades of persistence, scientists have recently developed facilities which can measure the vibrations of spacetime caused by astrophysical cataclysms such as the mergers of black holes and neutron stars. The first few detections have presented interesting astrophysical questions and it is clear that with an increase in the number and capability of ground-based facilities, gravitational waves will become an important tool for astronomy. A space-based observatory will complement these efforts by providing access to the milliHertz gravitational wave band, which is expected to be rich in both number and variety of sources. The European Space Agency (ESA) has recently selected the Laser Interferometer Space Antenna (LISA) as a Large-Class mission in its Cosmic Visions Programme. The modern LISA retains the basic design features of previous incarnations and, like its predecessor, is expected to be a collaboration between ESA, NASA, and a number of European National Agencies. In this talk, I will present an overview of the current LISA design, its scientific capabilities, and the timeline to launch.   

Pulsar Timing Arrays: Building a Low-Frequency Gravitational Wave Detector

Pulsars are rapidly rotating neutron stars with phenomenal rotational stability that can be used as celestial clocks in a variety of fundamental physics experiments. One of these experiments involves using a "pulsar timing array" of precisely timed millisecond pulsars to detect perturbations due to gravitational waves. The low-frequency gravitational waves detectable through pulsar timing will most likely result from an ensemble of supermassive black hole binaries.  I will introduce the efforts of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration which monitors an array of over 70 millisecond pulsars with the Green Bank Telescope and Arecibo Observatory, with a focus on our observation and data analysis methods. I will also describe how NANOGrav works with international partners through the International Pulsar Timing Array to build a low-frequency gravitational wave detector of higher sensitivity than any one pulsar timing array.   

Pulsar Timing Arrays: New Advances Toward Detecting Low-frequency Gravitational Waves

The gravitational wave landscape is expansive and ripe for discovery, offering unparalleled insights into a huge variety of astrophysical systems. Pulsar Timing Arrays (PTAs) exploit the exquisite rotational stability of millisecond pulsars to forge a galactic network of clocks, capable of registering the correlated influence of passing extragalactic gravitational waves. At nanohertz frequencies (where PTAs are sensitive) the most promising target is the ensemble signal of many inspiraling supermassive black-hole binary systems throughout the Universe. A detection of this signal (or even a stringent constraint) can teach us much about the merger history of massive galaxies, the dynamical environments of galactic cores, and the scaling relationships between massive black holes and their host galaxies. I will discuss the latest advances toward detection (including new insights into Solar System dynamics from NANOGrav’s recent 11-year dataset), and the exciting astrophysical information that is accessible to PTAs.